Method for determining the temperature of an electrically heatable catalytic converter

Abstract

A method for determining the temperature of an electrically heatable catalytic converter having an electric heating element that includes a heating resistor, the electrical resistance of which changes as a function of the component temperature of the electrically heatable catalytic converter. This resistance is determined from the current intensity and the voltage at the electrically heatable catalytic converter, and is used to determine the component temperature of the catalytic converter, based on a characteristic curve stored in the control unit. The energization of the heating resistor for determining the component temperature takes place in each case for only a short time in order to minimize the energy input into the heating resistor and thus avoid overheating of the heating resistor. In addition, by use of the short time interval, the aim is to minimize the energy requirements for determining the component temperature of the electrically heatable catalytic converter.

Claims

1. A method for determining the temperature of an electrically heatable catalytic converter in an exhaust gas system of an internal combustion engine, wherein the electrically heatable catalytic converter includes a heating resistor having a temperature-dependent resistance, comprising: energizing the electric heating resistor by closing a switch in a circuit that connects a battery to the electric heating resistor, determining the component temperature of the electrically heatable catalytic converter from the temperature-dependent electrical resistance of the heating resistor, for a known current intensity and a known voltage, wherein the power input into the measuring circuit takes place by means of a down converter that is controlled by pulse width modulation, and measuring current intensity and voltage at least ten times within a pulse width modulation period.

2. The method according to claim 1, wherein determining the component temperature of the electrically heatable catalytic converter comprises determining the component temperature in an operating phase in which electrical heating is not provided.

3. The method according to claim 2, wherein the energization period for the resistance measurement is selected to be between 50 s and 200 s.

4. The method according to claim 1, further comprising determining a correction factor that takes into account a change in the electrical resistance of the heating resistor due to aging of the electrically heatable catalytic converter.

5. The method according to claim 1, wherein a temperature controller for the electrically heatable catalytic converter utilizes the down converter as a continuous current controller.

6. The method according to claim 1, wherein determining the component temperature of the electrically heatable catalytic converter takes into account the line resistance of the electrical conductor in addition to the electrical resistance of the heating resistor.

7. The method according to claim 1, wherein the resistance measurement is carried out using a four-wire measuring method.

8. An exhaust aftertreatment system for an internal combustion engine comprising: an exhaust gas system in which an electrically heatable catalytic converter is situated, and a control unit that is configured to carry out a method according to claim 1 when a machine-readable program code is executed by the control unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained below in exemplary embodiments with reference to the associated drawings, which show the following:

(2) FIG. 1 shows an internal combustion engine having an exhaust gas system in which an electrically heatable catalytic converter for exhaust aftertreatment of the combustion gases of the internal combustion engine is situated;

(3) FIG. 2 shows an electrical switching circuit for controlling an electric heating resistor for electrically heating a catalytic converter;

(4) FIG. 3 shows another electrical switching circuit for controlling an electric heating resistor of an electrically heatable catalytic converter;

(5) FIG. 4 shows a controller arrangement for temperature and current control for the electric heating resistor of the electrically heatable catalytic converter; and

(6) FIG. 5 shows another electrical switching circuit for controlling an electric heating resistor of an electrically heatable catalytic converter.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIG. 1 shows an internal combustion engine 10, the exhaust outlet 16 of which is connected to an exhaust gas system 20. The internal combustion engine 10 is preferably designed as a spark ignition internal combustion engine 10 according to the Otto principle, and has a plurality of combustion chambers 12, on each of which at least one spark plug 14 for igniting an ignitable fuel-air mixture is situated. Alternatively, the internal combustion engine 10 may be designed as an auto-ignition internal combustion engine according to the Diesel principle. The internal combustion engine 10 is preferably designed as an internal combustion engine 10 that is supercharged by means of an exhaust gas turbocharger 18. Alternatively, the internal combustion engine 10 may be designed as a naturally aspirated engine that is not supercharged, or as an internal combustion engine 10 that is supercharged by means of a compressor or an electric compressor. The exhaust gas system 20 includes an exhaust duct 26, with a turbine 22 of the exhaust gas turbocharger near the engine, and downstream from the turbine 22 a catalytic converter 24 near the engine, and further downstream, preferably in the underbody position of a motor vehicle, a second catalytic converter 28, being situated in the flow direction of an exhaust gas through the exhaust gas system 20. At least one of the catalytic converters is designed as an electrically heatable catalytic converter 24, 28, preferably as an electrically heatable three-way catalytic converter or as an electrically heatable four-way catalytic converter 38. Alternatively, the electrically heatable catalytic converter 24, 28 may be designed as an SCR catalytic converter or as some other exhaust aftertreatment component. At least one of the catalytic converters 24, 28, 38 has an electric heating element 30, 32, in particular a heating disk, with which the catalytic converter 24, 28, 38 may be heated independently of the exhaust gas flow of the internal combustion engine 10. For this purpose, the electric heating elements 30, 32 are connected to a control unit 40 of the internal combustion engine 10 via signal lines 34, 36, respectively.

(8) FIG. 2 illustrates an electrical switching circuit for the electric heating element 30, 32, in particular for a heating resistor 48. The switching circuit includes a circuit 44 that connects a battery 42 of the motor vehicle to the electric heating resistor 48. The electric heating resistor 48, as a metal foil or metal wire, is preferably integrated into the substrate material of the electrically heatable catalytic converter 24, 28, 38. In addition, the switching circuit has a switch 46 with which the power supply to the heating resistor 48 may be easily interrupted or activated. The battery 42 may be, for example, a 12-volt battery or a 48-volt battery of a motor vehicle having an internal combustion engine. Alternatively, in a hybrid vehicle the battery 42 may be the high-voltage battery for the electric drive motor. The voltage UR at the heating resistor 48 is preferably sampled by a microcontroller pc. The current intensity IR is preferably measured by shunts or by a current transformer in combination with a microcontroller pc. The switch 46 is designed as a relay or as a MOSFET, for example. The heating resistance R results from the voltage U.sub.R and the current intensity I.sub.R via the relationship R=U.sub.R/I.sub.R. The component temperature of the electrically heatable catalytic converter 24, 28, 38 is then a function of the resistance R, which changes as a function of the temperature of the catalytic converter 24, 28, 38. In the simplest case, the energization of the electric heating resistor 48 may take place by temporarily switching on the circuit 44. When the desired component temperature of the electrically heatable catalytic converter 24, 28, 38 is reached or a certain time period has elapsed, the circuit 44 is reopened by opening the switch 46. By briefly energizing the electric heating resistor 48, a resistance measurement may also be carried out during operating phases in which the catalytic converter 24, 28, 38 is not to be heated. The measurement phases should be designed to be short enough to keep the energy input into the heating resistor 48 low. Overheating of the heating resistor 48 and excessive power consumption are thus avoided.

(9) An average component temperature is determined using the proposed method. The average component temperature is based on measurement, and is therefore robust against environmental influences that cannot be taken into account via a model calculation in a determination of the component temperature. Aging effects of the electric heating resistor 48 may be adapted when the resistance is determined for components having relevant aging, and at a known ambient temperature.

(10) Clocked opening and closing of the switch 46 results in a clocked voltage U and a clocked current intensity I, which may be interpreted as an average voltage and an average current intensity, respectively. The clocking may take place similarly as for pulse width modulation clocking, such as with the down converter, or with a lower clock frequency. Such a measurement typically takes place during the switch-on phase of the electrically heatable catalytic converter 24, 28, 38 after the cold start of the internal combustion engine 10.

(11) FIG. 3 illustrates a preferred exemplary embodiment of the electrical circuit 44 for heating the electrically heatable catalytic converter 24, 28, 38. Any desired power input between zero and maximum power may be provided by use of a pulse width modulation-controlled down converter that is preferably designed with MOSFET switches 46, 50. Compared to the exemplary embodiment illustrated in FIG. 2, the circuit 44 additionally includes a second switch 50 and an inductor, in particular a coil 54. Control of the electric current also requires it to be measured. The measurement of the current intensity I.sub.R and the voltage U.sub.R should take place at least ten times within a pulse width modulation period to allow good averaging. The component temperature of the electrically heatable catalytic converter via the temperature-dependent electrical resistance R of the heating resistor 48 may be determined, for example, by switching on the switch 46 once for a duration of at least five times the electrical system time constant, or by clocked switching multiple times with a small pulse width modulation ratio.

(12) FIG. 4 shows a refinement of the measuring arrangement illustrated in FIG. 3. Temperature control 60 for the electrically heatable catalytic converter 24, 28, 38 takes place, and the down converter illustrated in FIG. 3 is utilized as a continuous current controller 58.

(13) FIG. 5 illustrates another exemplary embodiment of a circuit 44 for heating the electrically heatable catalytic converter 24, 28, 38. Since in actual operation, in addition to the electrical resistance R of the heating resistor 48 the lines also have an electrical resistance 52, 56, these resistances 52, 56 may also be taken into account. The line resistances and contact resistances may be compensated for in a suitable manner within the scope of calculating the electrical resistance R of the heating resistor 48. In the simplest form, the line resistances are assumed to be constant and are subtracted from the measured resistance R. A so-called four wire measuring method, illustrated in FIG. 5, is recommended if the measuring accuracy is to be further increased during the determination of the electrical resistance R of the electrically heatable catalytic converter 24, 28, 38. This does not fundamentally change the measurement and control process, but the expected measuring accuracy for the resistance measurement is increased. The deviation in the component temperature of the electrically heatable catalytic converter 24, 28, 38 during the temperature determination may also be further reduced in this way.

LIST OF REFERENCE NUMERALS

(14) 10 internal combustion engine

(15) 12 combustion chamber

(16) 14 spark plug

(17) 16 exhaust outlet

(18) 18 exhaust gas turbocharger

(19) 20 exhaust gas system

(20) 22 turbine

(21) 24 catalytic converter near the engine

(22) 26 exhaust duct

(23) 28 second catalytic converter

(24) 30 first heating element

(25) 32 second heating element

(26) 34 signal line

(27) 36 signal line

(28) 38 four-way catalytic converter

(29) 40 control unit

(30) 42 battery

(31) 44 circuit

(32) 46 first switch

(33) 48 heating resistor

(34) 50 second switch

(35) 52 line resistance

(36) 54 coil

(37) 56 second line resistance

(38) 58 current controller

(39) 60 temperature controller

(40) I current intensity

(41) L coil

(42) R resistance

(43) S switch

(44) U voltage

(45) t time